Screens are used downhole to hold back solids during production from a given productive zone. Such zones can be very long and can be in cased or open hole. In the past screen sections, which can be about 10 meters long are connected together to span the productive interval. In an effort to equalize flow along a long interval, individual screen sections have been outfitted with devices to resist flow in unequal amounts so as to insure flow that is reasonably uniform over the extended interval. Such screen sections are made by Baker Oil Tools under the brand Equalizer®. They feature an annular space between the cylindrical screen and an underlying base pipe. Once the flow gets through the screen it goes axially along the base pipe which has no openings under the cylindrical screen section except an axial passage into a housing formed over the base pipe and to one side of the cylindrical screen section. The passage to the housing from under the cylindrical screen can involve a flow restriction, such as a spiral path. Spiral paths in different screen sections can get less restrictive to a given flow rate as the screen sections get further from the surface of the well, or be set to create equal resistance over the entire interval. In that way they equalize flow over a long interval.
More recently, there has been an interest developed in being able to sense whether liquid or gas is being produced into a screen and to provide valving to sense this change with a goal of admitting the liquid flow and cutting off the flow if gas is produced. Several such valves have been developed that can make this distinction and their internal construction is not the focus of the present invention. Rather, with the advent of the designs that can operate in different positions depending on whether liquid or gas flows through them, there have arisen problems that relate to how the components can be assembled for reliable operation, how the overall construction can be optimized for lower assembly cost and how one or a series of such screens can accommodate a need to kill a well and still function reliably thereafter, to name some of the more significant issues.
One issue with these valves is how to mount them in a manner where they don't leak. Threading the wall of the base pipe so that the valve assembly can be screwed in has built in leakage potential that a thread sealant does not fully resolve. The base pipe wall only allows so many thread turns and that has been a cause for concern regarding leakage. Welding the valve into a hole in the base pipe is not a viable option either as the valve components are sensitive to heat created during the welding process so as to make the operation of a welded into position valve somewhat uncertain. Removal of the valve at a later time without destroying it was also an issue. An alternative way to mount these valves so as to minimize or eliminate the risk from thread leaks was developed as part of the present invention.
These valves had narrow tortuous paths through them. One problem with them arose when there was a need to kill the well. Frequently, a well killing technique that was used with screens in the assembly was to pump down slurry into the base pipe to block the narrow slots within the base pipe where the filtered produced liquids would enter the base pipe. The problem with the valves that discriminate between liquid and gas flow was that solids that get to their internal passages would prevent them from operating later when it was time to bring the well in again after killing it. The manner that these valves were mounted left their internal components exposed to slurry used to kill the well from within the base pipe. Accordingly, another aspect of the present invention is to equip such valve ends that are exposed to the inside of the base pipe with a device to hold back the slurry used to kill the well so that the well could later be brought back on line without internal component blockage or damage from the slurry used to kill the well.
The proposed assembly technique for these screens was to mimic the assembly of the Baker Oil Tools Equalizer® screen. What was proposed was a base pipe opening offset from the cylindrical screen section. The base pipe would not be perforated under the cylindrical screen section but rather there would be an adjacent housing over the base pipe and to one side of the cylindrical screen section with an axial passage from the annular space under the cylindrical screen section to the housing. Before assembling the housing over the hole that would accept the valve that would let liquids pass but keep gases out, the valve would be screwed into the threaded hole made to accept it and then the housing would be slipped over it and sealed to the base pipe leaving open an axial passage or passages into the housing so that filtered liquids could go through the screen then through the valve and into the base pipe to be produced at the surface. Another aspect of the invention involves an assembly where the valve is installed in the base pipe and the side housing is eliminated in favor of simply mounting the valve so that its extension through the outer surface of the base pipe is small enough or flush so that the cylindrical screen section can be placed right over the valve and secured to the base pipe to simplify the time and cost of assembly of a screen section. These and other advantages of the present invention will be more readily appreciated by those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the claims represent the full scope of the invention.